It is widely held that healing and/or structural correction is greatly facilitated when a bone is stabilized in the proper position. Various devices for stabilization of bone are well known and routinely practiced in the medical arts. For example, an abnormal spine can be stabilized using a substantially rigid or semi-rigid interconnecting means (rod or plate) and fastening means (screws, clamps, hooks, claws, anchors, or bolts). Multiple fasteners are placed into the spinal pedicle of each vertebra and linked by at least one interconnecting means. One of the more difficult aspects is the surgical insertion of the interconnecting means along a fixed path of delivery longitudinally along the vertebrae and through each of the multiple fastening means between multiple vertebrae. Once in place, this system substantially immobilizes the spine and promotes bony fusion (arthrodesis).
Traditionally, the surgical techniques for stabilization of bone required large incisions (upwards of 6 cm in length) and a considerable amount of muscle to be cut and stripped away (retracted) from the bone for an “open” visualization of the bone and access thereto for the placement of the fasteners and instrument implantation. Although this so-called “open” surgical technique has successfully treated non-unions, instability, injuries and disease of the spine, it is not without disadvantages. Given the invasive nature of this technique, a lengthy healing time and considerable post-operative pain for the patient is common.
In response to aforementioned drawbacks, the surgical arts have developed minimally invasive systems and procedures intended to replace the more traditional open surgeries. Obviously, a less extensive system and procedure will eliminate the need to perform much of the cutting and stripping of muscle, resulting in reduced recovery time and less post-operative pain. As a result, percutaneous procedures have been developed which insert instruments and perform operations through small skin incisions, usually between 1.5 and 5 cm in length, thereby reducing soft tissue damage. However, smaller skin incisions and smaller surgical fields require more novel and innovative approaches to perform these complicated surgeries.
One such example of a minimally invasive system is the SEXTANT Spinal System by Medtronic (Memphis, Tenn.). This device is comprised of two basic components, screw extenders, and the rod inserter, which results in an instrument that looks like a sextant used in naval navigation. The device is an insertion tool that allows fasteners and interconnecting means to be applied to the spine in a minimally invasive manner. The screw extenders are long shafts used to deliver and attach screws to the vertebrae through small skin incisions. During surgery, these extenders protrude outside the body, allowing the surgeon to arrange and join their ends so that the rod inserter may be attached. The rod inserter is an arc-shaped arm that swings along a fixed axis and pushes an interconnecting rod though the skin and muscle and into the heads of the implanted fasteners (pedicle screws).
While the aforementioned technique is adequate when the fastening means are well aligned, it fails to deliver the rod when one of the screws is misaligned. Moreover, the interconnecting rod must be pushed by the surgeon along a fixed arch and cannot be directed around neural structures or bony obstructions. One consequence of forcibly pushing the rod through the fastening means is the possibility of collision between the rod and a bony obstruction, causing a piece of bone to break off, resulting in possible neurological damage. Another common problem is the interconnecting rod becoming disengaged from the rod inserter. When either of these incidents happens, additional surgery is often required to remove the bone fragment and rod from the wound. This may result in the surgeon abandoning the minimally invasive approach and reverting to a traditional approach. Current spinal implant systems do not allow the contour of the rod to match the normal curvature of the surrounding anatomy, and such systems are not customizable to meet the individual anatomical variables that each patient presents.
In order to help avoid damaging sensitive anatomy and expedite implant assembly, various image-based navigation systems have been employed which utilize patient images obtained prior to or during the medical procedure to guide a surgeon during the surgery. Recent advances in imaging technology have produced detailed two and three dimensional images using optically guided, fluoroscopic guided, and electromagnetic field based systems. These image-based systems have also been used in combination with the previously described “open” surgeries. One significant problem with most image-based systems is that the radiation generated is transmitted to the patient and surgical staff, which may result in physiological damage over time. Also, the cost and portability of this equipment continue to be an issue. In addition, these systems often require the surgeon to undergo extensive training to operate correctly.
Accordingly, a need exists in the surgical arts for a system and minimally invasive procedure capable of providing optimal mechanical support and bony fusion, while reducing the likelihood of bone damage and neural functioning when compared to the currently available interconnecting elements. It is also desirable to provide a surgical procedure that can be performed in conjunction with, but does not require, an image-based tracking system.